Recovering Labels from Local Updates in Federated Learning

TL;DR

This paper introduces RLU, a novel label recovery method for federated learning that accurately reconstructs data labels even under realistic conditions, enhancing gradient inversion attack effectiveness.

Contribution

RLU is a new label recovery scheme that works effectively in real-world federated learning scenarios with multiple local epochs, data heterogeneity, and various optimizers.

Findings

RLU achieves near-perfect label recovery on untrained models.

RLU outperforms existing methods across multiple datasets and scenarios.

Reconstructed images show improved quality in gradient inversion attacks.

Abstract

Gradient inversion (GI) attacks present a threat to the privacy of clients in federated learning (FL) by aiming to enable reconstruction of the clients' data from communicated model updates. A number of such techniques attempts to accelerate data recovery by first reconstructing labels of the samples used in local training. However, existing label extraction methods make strong assumptions that typically do not hold in realistic FL settings. In this paper we present a novel label recovery scheme, Recovering Labels from Local Updates (RLU), which provides near-perfect accuracy when attacking untrained (most vulnerable) models. More significantly, RLU achieves high performance even in realistic real-world settings where the clients in an FL system run multiple local epochs, train on heterogeneous data, and deploy various optimizers to minimize different objective functions. Specifically, RLU estimates labels by solving a least-square problem that emerges from the analysis of the correlation between labels of the data points used in a training round and the resulting update of the output layer. The experimental results on several datasets, architectures, and data heterogeneity scenarios demonstrate that the proposed method consistently outperforms existing baselines, and helps improve quality of the reconstructed images in GI attacks in terms of both PSNR and LPIPS.